WASHINGTON — Under a canopy of poplar and oak trees, a team of geophysicists surveyed the forest floor for century-old wartime relics. They positioned an electromagnetic scanner atop the carpet of leaves while the delicate instrument harvested data about objects in the soil beneath.

In 1918, mortars and artillery shells arched toward this spot near the Dalecarlia Reservoir, one of the main water sources for the nation’s capital. But no armies fought here and no soldiers charged up the embankment. Rather, the shells were launched from the wartime research campus to the east at American University, where scientists developed chemical weapons, explosives, bombs and gas masks to use on the battlefields in World War I.

In this centennial of the war’s end, the team working in the woods was a reminder that the Great War had another name — “the Chemists’ War,” a sobriquet reflecting the crucial role of science in the conflict. Alex Zahl, a project manager for the United States Army Corps of Engineers and a self-described World War I buff, mused over the state-of-the-art science detecting remains of experiments dating to 1918.

“They were using cutting-edge technology 100 years ago developing chemical weapons,” Mr. Zahl, 62, said in the air-conditioned trailer that serves as the cleanup headquarters. “That was high technology at that time, and here we are 100 years later using high technology again to remediate the material left behind.”

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Contract surveyors with the Army Corps of Engineers' survey crew, Jake Vera, left, and Andrew Fedetz, right, using a magnetometer to scan the ground in the Dalecarlia Woods in the District of Columbia. The crew searched for ordnance or debris remaining from the nearby World War I chemical warfare research laboratory. CreditAndrew Mangum for The New York Times

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Aerial view of the American University Experiment Station, established in 1917 for developing chemical weapons and protective gear for chemical warfare.CreditNational Archives and Records Administration

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In the Spring Valley neighborhood of Washington, D.C., a home was demolished in 2012 because of contamination. Adjacent, the unoccupied residence of the American University president.CreditAndrew Mangum for The New York Times

World War I, which ended with the armistice on Nov. 11, 1918, is infamous for its horrific battlefield conditions, its grinding, bloody clashes — the Battles of the Somme, Verdun, Passchendaele and others — and the resulting human slaughter. Some 8.5 million soldiers were killed and 21 million more were wounded.

Less is remembered about the role of science. The war hastened technological progress with optics, radio and primitive sonar. The Germans’ largest siege cannon, the dreaded “Paris Gun,” heaved gigantic shells into the stratosphere that returned to earth to pummel the French capital, 75 miles away. Lithe German submarines prowled under the waves. Aviation, in its infancy at the war’s start, roared into maturity by the end. The inventor Thomas A. Edison lent his scientific prowess to the United States Navy.

Even before the United States entered the war, the National Academy of Sciences anticipated the need for collaboration among scientists, universities, industry and the military. President Wilson established the National Research Council in 1916, and after the president signed the war declaration on April 6, 1917, the National Academy’s foreign secretary, George E. Hale, fired off a telegram to counterparts in Britain, France, Italy and Russia: “The entrance of the United States into the war unites our men of science with yours in a common cause.”

American scientists threw themselves into the war effort. Though few are household names today, top physicists, chemists and engineers volunteered. Many from prestigious universities were known as “dollar-a-year men,” paid a symbolic wage for their efforts.

“The military had problems to solve that it couldn’t solve on its own,” said Daniel J. Kevles, emeritus professor of history at Yale and author of “The Physicists.”

In many ways, the United States Chemical Warfare Service epitomized such efforts. Germany’s chemical warfare program was the brainchild of its most esteemed chemists, and the Americans were ill-prepared. Entering the fray two years after Germany sparked the chemical arms race with a surprise chlorine gas attack in Flanders, Belgium, the United States Army had neither gas masks nor protective gear, and no capacity for producing or deploying chemical weapons. Doctors had no experience with gassed or chemically burned soldiers. And there was little time to catch up.

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An undated photo of a soldier's forearm comparing different blister agents. Soldiers stationed at the university in 1917 and 1918 underwent so-called "man tests."CreditNational Archives and Records Administration

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Protective suits at the American University experiment station.CreditNational Archives and Records Administration

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Mr. Fedetz, a contractor, carrying a newly developed “man portable vector” that can help distinguish between harmless buried objects and those that are potentially hazardous.CreditAndrew Mangum for The New York Times

To correct those deficiencies, the War Department set up a laboratory, initially under the civilian Bureau of Mines, called the American University Experiment Station. It began modestly with one building and fewer than 100 researchers.

By the war’s end, almost 2,000 soldiers, scientists and civilians worked at the campus, which soldiers called “Mustard Hill” for the blister agent sulfur mustard. The army leased nearby farmland for proving grounds, part of which the soldiers named “Death Valley.” The service had satellite labs and outposts on campuses and factories throughout the country — an effort that some historians compare to the Manhattan Project in World War II.

When the war ended, the scientists revealed they had developed a new weapon called lewisite, an arsenic-based blister agent manufactured outside Cleveland at a top-secret factory nicknamed “the mousetrap” because of its elaborate security. Though never used, the so-called “super-poison gas” was reportedly to be dropped on the Germans in 1919 if the war had not ended.

“Although they had many imperfect successes, the rise of chemical warfare within the U.S. military during World War I, I would say, is unparalleled,” said historian Thomas I. Faith, the author of a 2014 book about chemical warfare, “Behind the Gas Mask.”

The experiment station reverted to American University when the war ended. Over the decades, developers turned surrounding land into an affluent residential neighborhood, transforming “Death Valley” into Spring Valley, in the northern section of the District of Columbia. The WWI legacy was largely forgotten until 1993, when developers dug up a cache of mortars, triggering a state of emergency, evacuations and a lengthy cleanup. In all, 141 munitions were found at that site.

Several years later, the Corps of Engineers reopened its examination of the area, acknowledging that it had prematurely shut down the cleanup. The contamination and debris proved more extensive than originally believed, sparking an uproar from residents and a pledge from the Army for more transparency and community participation.

The corps has been a near-constant presence in Spring Valley since then. Hundreds of munitions have been hauled away, most of them from a handful of burial pits. Arsenic has been the most widespread chemical contaminant — the army has carted off thousands of tons of tainted soil and replaced it with clean topsoil. Sulfur mustard, lewisite and other chemical warfare compounds — as well as traces of the constituent chemicals that remain after the warfare agents break down over time — have also been detected and removed.

Concerns about the health effects of chemical contamination among Spring Valley’s roughly 25,000 residents have long lingered over the cleanup, especially after a lengthy neighborhood newspaper investigation reported unusual illnesses and health problems among residents.

A 2007 health study conducted by Johns Hopkins University School of Public Health for the city found the neighborhood’s residents to be generally healthier than most Americans, though with slightly more incidence of cancer — including some that can be linked to arsenic — compared to nearby Chevy Chase. A follow-up study in 2013 similarly found that the community’s health was very good. Finding no conclusive links between the war era and disease, it recommended no further epidemiological study but did recommend continued health monitoring in the neighborhood.

The environmental cleanup is also a kind of archaeological undertaking, a historical scavenger hunt for evidence of the scientific enterprise around chemical warfare.

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American University’s recreational complex on the edge of the Spring Valley neighborhood.CreditAndrew Mangum for The New York Times

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An historical photo of a test explosion of a shrapnel bomb at the university’s experiment station.CreditNational Archives and Records Administration

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A soldier testing a flamethrower.CreditNational Archives and Records Administration

One hot spot was a contaminated property where the Corps razed a house in 2012. The location has remained a stubborn symbol of the cleanup’s complexities. In summer 2017, during what was expected to be a low-risk phase, an unidentified chemical agent in the soil sickened three contractors, halting the excavation.

Air samples from under the adjacent residence, which had been vacated last year by the previous university president, found traces of chemicals. The excavation work resumed last month. The current president, Sylvia M. Burwell, former secretary of Health and Human Services, does not live there. The university declined a request to interview Ms. Burwell.

In the latest cleanup phase, the Army has begun examining the soil of about 91 properties beneath the cone of the artillery range. The scanning near the reservoir was at an early stage, using new technology that pinpoints buried metal objects and compares their digital profiles against a database of military munitions, such as mortar shells or 75-millimeter artillery rounds. If the item is deemed harmless “cultural debris,” in Army parlance — a discarded soda can, for example — then it won’t be disturbed.

“We’re going to leave items in the ground that all this equipment says is cultural debris and nothing to do with World War I activities,” Mr. Zahl said.

On one Spring Valley property, some relics will likely never be removed. Last year, Elliot Gerson and his wife, Jessica Herzstein, bought the stately home where Ms. Herzstein’s parents had lived for decades. The Corps has extensively investigated and cleaned up the property and says it has no health concerns. But three original structures from the Experiment Station remain.

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Soldiers wearing masks in the test trenches that were used for experiments. The trenches were filled in, the land later sold to developers.CreditNational Archives and Records Administration

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Apparatus for testing peripheral vision through a gas mask.CreditNational Archives and Records Administration

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Elliot Gerson, a resident of the Spring Valley neighborhood, entering one of the concrete bunkers that remain on his property from the WWI experiments.CreditAndrew Mangum for The New York Times

On the wooded slope above the driveway, weeds choke a concrete platform with an angled gutter in the middle — the launching pad for the experimental mortar range. Behind the house, two ivy-draped bunkers nestle in the woods, ferns poking through cracks.

One afternoon, Mr. Gerson, 66, paused to reflect midway down a slate path leading to one of the structures. He called them “a secret archaeological site in the forest,” evidence of century-old scientific endeavors.

Inside, he pointed to holes in the walls where scientists might have pumped gas into the chamber. Though harmless now, he said, the structure is a memento of the ghoulish weapons tested here, and newly revived from obsolescence in Syria and elsewhere 100 years after the war’s end.

“They’re still fascinating reminders of a remarkably little-known but important chapter in American history. Some of the best chemists in the United States were assembled here in an urgent effort to save the Allies after the German use of chemical weapons,” he said.

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One of the WWI concrete bunkers.CreditAndrew Mangum for The New York Times